Commit 48be69a0 authored by Russell King's avatar Russell King

ARM: move signal handlers into a vdso-like page

Move the signal handlers into a VDSO page rather than keeping them in
the vectors page.  This allows us to place them randomly within this
page, and also map the page at a random location within userspace
further protecting these code fragments from ROP attacks.  The new
VDSO page is also poisoned in the same way as the vector page.
Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
parent f6f91b0d
......@@ -130,4 +130,8 @@ struct mm_struct;
extern unsigned long arch_randomize_brk(struct mm_struct *mm);
#define arch_randomize_brk arch_randomize_brk
#define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
struct linux_binprm;
int arch_setup_additional_pages(struct linux_binprm *, int);
#endif
......@@ -8,6 +8,7 @@ typedef struct {
atomic64_t id;
#endif
unsigned int vmalloc_seq;
unsigned long sigpage;
} mm_context_t;
#ifdef CONFIG_CPU_HAS_ASID
......
......@@ -428,8 +428,8 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
#ifdef CONFIG_MMU
/*
* The vectors page is always readable from user space for the
* atomic helpers and the signal restart code. Insert it into the
* gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
* atomic helpers. Insert it into the gate_vma so that it is visible
* through ptrace and /proc/<pid>/mem.
*/
static struct vm_area_struct gate_vma = {
.vm_start = 0xffff0000,
......@@ -461,6 +461,40 @@ int in_gate_area_no_mm(unsigned long addr)
const char *arch_vma_name(struct vm_area_struct *vma)
{
return (vma == &gate_vma) ? "[vectors]" : NULL;
return (vma == &gate_vma) ? "[vectors]" :
(vma->vm_mm && vma->vm_start == vma->vm_mm->context.sigpage) ?
"[sigpage]" : NULL;
}
extern struct page *get_signal_page(void);
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
struct mm_struct *mm = current->mm;
struct page *page;
unsigned long addr;
int ret;
page = get_signal_page();
if (!page)
return -ENOMEM;
down_write(&mm->mmap_sem);
addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
if (IS_ERR_VALUE(addr)) {
ret = addr;
goto up_fail;
}
ret = install_special_mapping(mm, addr, PAGE_SIZE,
VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
&page);
if (ret == 0)
mm->context.sigpage = addr;
up_fail:
up_write(&mm->mmap_sem);
return ret;
}
#endif
......@@ -8,6 +8,7 @@
* published by the Free Software Foundation.
*/
#include <linux/errno.h>
#include <linux/random.h>
#include <linux/signal.h>
#include <linux/personality.h>
#include <linux/uaccess.h>
......@@ -15,12 +16,11 @@
#include <asm/elf.h>
#include <asm/cacheflush.h>
#include <asm/traps.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
#include <asm/vfp.h>
#include "signal.h"
/*
* For ARM syscalls, we encode the syscall number into the instruction.
*/
......@@ -40,11 +40,13 @@
#define SWI_THUMB_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
#define SWI_THUMB_RT_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
const unsigned long sigreturn_codes[7] = {
static const unsigned long sigreturn_codes[7] = {
MOV_R7_NR_SIGRETURN, SWI_SYS_SIGRETURN, SWI_THUMB_SIGRETURN,
MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
};
static unsigned long signal_return_offset;
#ifdef CONFIG_CRUNCH
static int preserve_crunch_context(struct crunch_sigframe __user *frame)
{
......@@ -401,12 +403,15 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
return 1;
if ((cpsr & MODE32_BIT) && !IS_ENABLED(CONFIG_ARM_MPU)) {
struct mm_struct *mm = current->mm;
/*
* 32-bit code can use the new high-page
* signal return code support except when the MPU has
* protected the vectors page from PL0
* 32-bit code can use the signal return page
* except when the MPU has protected the vectors
* page from PL0
*/
retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
retcode = mm->context.sigpage + signal_return_offset +
(idx << 2) + thumb;
} else {
/*
* Ensure that the instruction cache sees
......@@ -608,3 +613,36 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
} while (thread_flags & _TIF_WORK_MASK);
return 0;
}
static struct page *signal_page;
struct page *get_signal_page(void)
{
if (!signal_page) {
unsigned long ptr;
unsigned offset;
void *addr;
signal_page = alloc_pages(GFP_KERNEL, 0);
if (!signal_page)
return NULL;
addr = page_address(signal_page);
/* Give the signal return code some randomness */
offset = 0x200 + (get_random_int() & 0x7fc);
signal_return_offset = offset;
/*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
ptr = (unsigned long)addr + offset;
flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
}
return signal_page;
}
/*
* linux/arch/arm/kernel/signal.h
*
* Copyright (C) 2005-2009 Russell King.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#define KERN_SIGRETURN_CODE (CONFIG_VECTORS_BASE + 0x00000500)
extern const unsigned long sigreturn_codes[7];
......@@ -35,8 +35,6 @@
#include <asm/tls.h>
#include <asm/system_misc.h>
#include "signal.h"
static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };
void *vectors_page;
......@@ -850,13 +848,6 @@ void __init early_trap_init(void *vectors_base)
kuser_init(vectors_base);
/*
* Copy signal return handlers into the vector page, and
* set sigreturn to be a pointer to these.
*/
memcpy((void *)(vectors + KERN_SIGRETURN_CODE - CONFIG_VECTORS_BASE),
sigreturn_codes, sizeof(sigreturn_codes));
flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
#else /* ifndef CONFIG_CPU_V7M */
......
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